Politicians and celebrities joined cancer campaigners on Wednesday to condemn New York governor Andrew Cuomo's proposal to allow the controversial gas drilling technique known as fracking in the state.

At the first of two public hearings in New York City over the plan to end the ban on fracking, the state authorities were left in little doubt about the scale of the opposition. Speakers at the packed and often unruly meeting in the 900-seat Tribeca performing arts centre were overwhelmingly against the technique, which involves blasting chemical-laden water and sand into shale rock to release gas.

Many of the speakers condemned the hearings themselves as a sham, because they said they were set up to allow public comment about draft regulations, before any environmental assessment had been carried out.

Senators and other elected officials said the process had "too many unknowns, both financially and environmentally" to begin drilling. Environmental groups blame fracking for contaminating water wells and threatening the safety of communities.

Addressing a crowd of residents, activists and others outside the hearing, Senator Tony Avella, the Democrat author of a bill which would prohibit fracking in New York state, said: "I urge the Department of Conservation and the governor to pause in their deliberations and take full measure of the risks versus the 'gold rush industry' and make the right decision for this state for generations to come."

He added: "The risk of catastrophic danger to the environment, the health of New York residents and adverse economic impacts that result from hydraulic fracturing far outweigh the potential for job creation and promotion of a natural gas alternative for oil."

Mark Ruffalo, the actor, said: "The more we learn about fracking the more we see that natural gas is not a clean transition fuel, but a bridge to nowhere. The future of New York state depends on the action and resolve of the citizens of today – to reject this dangerous process and build a sustainable future for our children."

Opponents of the drilling method criticised the Cuomo administration for exaggerating the economic benefits. They questioned the number of jobs that would be created, and said the administration had failed to consider the negative impacts on agriculture, tourism and other industries. Fracking has been estimated to create up to 25,000 jobs directly and double that in related jobs in New York state alone, according to a fact sheet from the New York Department of Environmental Conservation. The iindustry insists fracking is safe.

Laura Weinberg, president of the Great Neck Breast Cancer Coaltion, called fracking a "direct assault on the cancer community of New York".

"If fracking is approved our collective past efforts to protect public health in New York state are washed away as residents will be exposed to the very same carcinogen and endocrine disrupting chemical that we have fought to ban," she said.

At the hearing on Wednesday, a series organised by the NYDEC to allow public input into its regulations for the state, the process itself was called into question.

Josh Fox, the director of the award-winning documentary Gasland, which showed flaming kitchen taps in one scene looking at the environmental effects of the process, addressed the hearing by speaking directly to the DEC. Fox, who acknowledged his film had "opened the floodgates" of opposition to fracking, described the hearing as a "charade" and said: "Your premise is wrong. Your premise is how should we frack New York."

Instead, he said, the premise should be not to do it at all. "Clearly fracking should be banned in New York state" he said.

Others echoed his sentiments and said that the process of developing regulations should not be going on at the same time as an environmental impact assessment.

To cheers, Jessica Roff, from New York, said: "Governor Cuomo it is your responsibility to protect the people of New York state and we will be here until you do."

Cuomo hopes to echo the energy boom that Pennsylvania has seen in recent years because of drilling in the Marcellus Shale formation – the largest US deposit of natural gas – which stretches from New York to parts of Pennsylvania, West Virginia and Ohio. He hopes to end a drilling ban in the state by next year.

Speakers, who were each given three minutes to speak, were overwhelmingly against fracking, but one man from a lobbying group called the New York Affordable Reliable Energy Alliance spoke of the need for jobs in the "empty stores and dead villages" of upstate New York.

Cathy Ann Kerry, from the New York State Petroleum Council, one of a few industry spokespersons who approached reporters outside the hearing, said that the "armageddon" predicted by environmentalists hadn't happened.

Referring to the safety and environmental risks she said: "This has been overly exaggerated. We've been drilling in this state for six years with no incidents. That speaks volumes of the DEC's ability to inspect and regulate." She said the chemicals involved in hydrofracking were "minimal".

A spokeswoman for the New York Department for Environmental Conservation said the 90-day hearing process would remain open for written comments up to 11 January.